From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0D37CC433B4 for ; Thu, 29 Apr 2021 15:02:51 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 439A06143B for ; Thu, 29 Apr 2021 15:02:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 439A06143B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:56286 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lc8Bl-0007LS-0q for qemu-devel@archiver.kernel.org; Thu, 29 Apr 2021 11:02:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55006) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lc8AJ-0006Nc-VL for qemu-devel@nongnu.org; Thu, 29 Apr 2021 11:01:20 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:29906) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lc8AC-0007ha-Fy for qemu-devel@nongnu.org; Thu, 29 Apr 2021 11:01:19 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619708463; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NeFzO8oi1a/ZP3+HXtZWR4VXqHHXQGuUzUtcIpnS4VY=; b=WNLOmGQ3v+mmFmoORlSPOvIvQ2ZfUKoK2ZZmSSuyJvS/fgjOTJbLiHhqdaH16QyYhUPnhc aH7D+k2qbUB4h0guK776cJbClP3oZvPP6gmhq/Pqh6JxnanRCj2LaCEOEtfZxjXJH72Zmp coK5V5ZeSciLS8d4hTYq8vQttI0rerI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-198-iz_yuyyqMoWGHTd3tGrryg-1; Thu, 29 Apr 2021 11:00:59 -0400 X-MC-Unique: iz_yuyyqMoWGHTd3tGrryg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1CDF76D258; Thu, 29 Apr 2021 15:00:58 +0000 (UTC) Received: from localhost (ovpn-114-114.ams2.redhat.com [10.36.114.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id 41FB719C45; Thu, 29 Apr 2021 15:00:39 +0000 (UTC) Date: Thu, 29 Apr 2021 16:00:38 +0100 From: "Richard W.M. Jones" To: Stefan Hajnoczi Subject: Re: [ANNOUNCE] libblkio v0.1.0 preview release Message-ID: <20210429150038.GT26415@redhat.com> References: <20210429142259.GR26415@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=rjones@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.22, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , pkrempa@redhat.com, Alberto Garcia , slp@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com, Vladimir Sementsov-Ogievskiy , Klaus Jensen , philmd@redhat.com, Markus Armbruster , sgarzare@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Apr 29, 2021 at 03:41:29PM +0100, Stefan Hajnoczi wrote: > On Thu, Apr 29, 2021 at 03:22:59PM +0100, Richard W.M. Jones wrote: > > On Thu, Apr 29, 2021 at 03:05:50PM +0100, Stefan Hajnoczi wrote: > > > The purpose of this preview release is to discuss both the API design > > > and general direction of the project. API documentation is available > > > here: > > > > > > https://gitlab.com/libblkio/libblkio/-/blob/v0.1.0/docs/blkio.rst > > > > libvirt originally, and now libnbd, keep a per-thread error message > > (stored in thread-local storage). It's a lot nicer than having to > > pass &errmsg to every function. You can just write: > > > > if (nbd_connect_tcp (nbd, "remote", "nbd") == -1) { > > fprintf (stderr, > > "failed to connect to remote server: %s (errno = %d)\n", > > nbd_get_error (), nbd_get_errno ()); > > exit (EXIT_FAILURE); > > } > > > > (https://libguestfs.org/libnbd.3.html#ERROR-HANDLING) > > > > It means you can extend the range of error information available in > > future. Also you can return a 'const char *' and the application > > doesn't have to worry about lifetimes, at least in the common case. > > Thanks for sharing the idea, I think it would work well for libblkio > too. > > Do you ignore the dlclose(3) memory leak? I believe this mechanism in libnbd ensures there is no leak in the ordinary shared library (not dlopen/dlclose) case: https://gitlab.com/nbdkit/libnbd/-/blob/f9257a9fdc68706a4079deb4ced61e1d468f28d6/lib/errors.c#L35 However I'm not sure what happens in the dlopen case, so I'm going to test that out now ... > > > Examples are available here: > > > > > > https://gitlab.com/libblkio/libblkio/-/tree/v0.1.0/examples > > > > > > The goal is to eventually include the following drivers: > > > - Linux io_uring > > > - NVMe (VFIO and vfio-user) > > > - virtio-blk (VFIO, vfio-user, vhost-user-blk, and vhost-vdpa-blk) > > > > > > There are a few reasons why libblkio is needed: > > > > > > 1. QEMU, Ceph, GlusterFS, MariaDB, and other programs have been adding > > > more low-level block I/O code, most of it duplicated. Usually only > > > one or two of Linux AIO, io_uring, userspace drivers, vhost-user > > > drivers, etc are implemented. This makes it difficult to benefit from > > > the latest advances in high-performance block I/O. > > > > > > 2. Coding to a standard API makes it possible to introduce new > > > optimizations or hardware interfaces without costly changes to the > > > software stack. > > > > > > 3. A client library is needed so applications can take advantage of > > > qemu-storage-daemon's vhost-user-blk exports. > > > > > > 4. Implementing block I/O as a library allows QEMU to use Rust for new > > > code without messy QEMU internal API bindings. Note that libblkio > > > currently does not provide a Rust crate, it only offers a C API. > > > > This is where I get confused about what this library actually does. > > It's not just a nicer wrapper around io_uring, but what is it actually > > doing? > > It's a library for what QEMU calls protocol drivers (POSIX files, > userspace NVMe driver, etc). In particular, anything offering > multi-queue block I/O fits into libblkio. > > It is not intended to replace libnbd or other network storage libraries. > libblkio's properties API is synchronous to keep things simple for > applications. Attaching to network storage needs to be asynchronous, > although the libblkio API could be extended if people want to support > network storage. I think what confuses me is why is NVMe any different from io_uring? ie would this work? $ blkio-info --output=json io_uring path=/dev/nvme0 Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/